Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. Atrial fibrillation is a common sustained cardiac arrhythmia and a major cause of stroke. This condition is perpetuated by reentrant wavelets propagating in an abnormal atrial-tissue substrate. Various approaches have been developed to interrupt wavelets, including surgical or catheter-mediated atriotomy. Prior to treating the condition, one has to first determine the location of the wavelets. Various techniques have been proposed for making such a determination, including the use of catheters with a distal assembly that is adapted to measure activity and/or ablate within a pulmonary vein, coronary sinus or other tubular structure about the inner circumference of the structure. One such distal assembly has a tubular structure comprising a generally circular main region generally transverse and distal to the catheter shaft and having an outer circumference of about 360 degrees and a generally straight distal region distal to the main region. The tubular structure comprises a non-conductive cover over at least the main region of the distal assembly. A support member having shape-memory is disposed within at least the main region of the mapping assembly. A plurality of electrode pairs, each comprising two ring electrodes, are carried by the generally circular main region of the distal assembly.
In use, the electrode catheter is inserted into a guiding sheath which has been positioned a major vein or artery, e.g., femoral artery, and guided into a chamber of the heart. Within the chamber, the catheter is extended past a distal end of the guiding sheath to expose the distal assembly. The catheter is maneuvered through movements that include deflection of a distal portion of the catheter so that the distal assembly is positioned at the tubular region in the heart chamber. The ability to control the exact position and orientation of the catheter and also the configuration of the distal assembly is critical and largely determines how useful the catheter is.
Deflection and steering of the catheter is typically accomplished by a control handle that houses deflection mechanism responsive to an actuator provided on the control handle. A puller wire extends through the catheter in a lumen along one side and the deflection mechanism draws on the puller wire proximally to deflect the catheter toward that side. Bi-directional deflection is accomplished by two opposing puller wires, each along one side of the catheter. By manipulating the actuator in one selected direction or another, the deflection mechanism acts on a selected puller wire to deflect the catheter along that side of the catheter. The distal end of each puller wire is typically anchored by means of a crimped ferrule soldered to a tip dome or a T-bar adhesive bonded to a diamond cut groove in a side wall of a tubing. However, these anchoring means can be offset from the lumens thus subject the puller wire to combined stresses of bending and shear along with tensile stresses. Moreover, tip deflection can also be skewed and off plane reducing predictability of desired deflection.
Another issue with catheters arises from free play and slippage between the support member of the distal assembly and the nonconductive cover which reduces the accuracy of the mapping and ablation procedures. Furthermore, the support member can also dislodge or detach from the catheter when the distal assembly is subjected to repeated and/or excessive contact forces. Additionally, repeated and/or excessive contact forces can also damage components, such as a location sensor, that are near where the support member is anchored to the catheter.
Accordingly, there is a desire for a catheter that provides bi-direction deflection in a manner that avoids bending and shearing stresses on the puller wires and a catheter that avoids skewing or off-plane deflection. There is also a desire for a catheter that minimizes micro-movements between the support member and the cover during mapping and ablation and a catheter with a distal assembly that is reliably mounted to the catheter.